Carbon nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. There are two general types of carbon nanotubes, referred to as multi-walled carbon nanotubes (MWNTs) and single-walleded carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
Single-walleded carbon nanotubes (SWNTs) exhibit interesting and useful electrical properties, and may be utilized for a variety of devices, such as integrated molecular electronic devices and others. In order to achieve such integration, it is often desirable to assemble individual SWNTs into desired architectures on substrates by placing them at specific locations with controlled orientations. One approach to the assembly of nanotubes includes controlled chemical synthesis. In this regard, patterned growth by chemical vapor deposition (CVD) can be used to control the locations of SWNTs on large flat substrates and on three-dimensional (3D) surface structures.
Accurately controlling the orientations of SWNTs continues to present challenges to the implementation of SWNTs in a variety of applications. For example, post-growth manipulation and assembly of SWNTs has not been very successful thus far due to factors including poor SWNT solubility in liquids and significant amounts of impurity particles in the nanotube materials. In addition, factors such as thermal and gas flow randomization can result in nanotube materials being formed in undesirable arrangements. Furthermore, when growing carbon nanotubes close to a substrate, the forces between the substrate and the carbon nanotubes tend to pull the nanotubes to the substrate as they are grown. These and other factors have presented challenges to the production of oriented nanotubes and to their integration with molecular electronic devices and others.